(FORTUNE Small Business) – In the 18 months since we wrote about Matt Dilling, the founder of Brooklyn's Lite Brite Neon Studio, he has doubled his company's workspace and annual revenue--to 4,000 square feet and $600,000. He's also saving $75 a month on gas. Last July, Dilling drove his 1979 Mercedes diesel up to Yestermorrow Design/Build School in Warren, Vt., where he converted his company car to run on used vegetable oil. By driving his staff and clients using free oil from a nearby burger joint (and Neon customer) called Schnack, Dilling has already managed to recoup his $850 engine-conversion cost. Dilling is not alone: Companies that convert cars and sell DIY conversion kits for diesels, such as Greasecar, Greasel Conversions, and Green Grease Monkey, have seen sales soar along with fuel prices. In New York, Dilling has a wide choice of suppliers--and octanes. "Supposedly the best oil is the canola oil from Indian food," he says. "Maybe it gives an extra afterburn."